"We, the Green Party, will work with local organisations and residents to oppose expansion.

"I am very concerned at decisions taken only in the interest of business and profit that disregard the consequences of this expansion on thousands of people in West London and Brentford in particular.

"Hounslow may well become the capital of respiratory disease in Britain as a result of high levels of air pollution."

Ms Scott had teamed up with Green Party colleague Victoria George to successfully apply for a £1,000 grant from Mapping for Change, a citizens' science project based at University College London (UCL).

The monitors which record nitrogen dioxide levels have been installed at sites around Brentford, including beside the A4 and M4, outside schools and at green spaces like Boston Manor Park, where they will remain until July 29.

They will then be sent to UCL for analysis, with the results expected back in September.

Ms Scott said the detailed information would be used to educate local schoolchildren about air pollution and to lobby the council and local MP Ruth Cadbury to take further steps to address the issue.

In recommending expansion at Heathrow, the Airports Commission said it believed a third runway could be built at the airport without breaching EU air quality limits in the area.

Critics including Ms Cadbury have questioned this assertion, pointing out that the legally-binding limit is already being breached at some local checkpoints.

Ms Scott is one of five candidates standing the Brentford by-election on Thursday (July 9). A profile of her and the other candidates is available here .